This longitudinal study investigated the relation between negative reactivity and attachment in children with Down syndrome (DS). Specifically, we examined whether extremely low negative reactivity is associated with the enactment and organization of attachment behaviors. To address this issue 30 infants with DS (13 female, 17 male) were observed in Ainsworth's Strange Situation at 19 and 27 months. The intensity and duration of distress reactions were coded in 15-s intervals throughout each Strange Situation episode. Children's distress intensity during separations from caregivers was used to place children into Low versus Moderate/High Negative Reactivity groups. In addition, ratings of infants' social interactive behaviors (contact maintenance, proximity seeking, distance interaction, resistance, and avoidance) were made for each episode and used to assess the quality of infants' attachment relationships. The data indicated that there are high rates of Type A and D insecure attachments within the DS population at each age studied. However, low negative reactivity was not consistently related to the activation of the attachment behavioral system, or associated with insecure attachment relationships. Alternative explanations for the high rate of insecure attachments are discussed.